With operator safety in mind, power equipment, particularly mowing machines, typically feature safety devices such as a blade brake clutch (BBC) control. A BBC can include a clutch that selectively engages a blade or blades associated with an engine output member. A brake can also be included that retards the rotation of the blade when the blade is disengaged from the engine output member. The combination of these two coupling devices permits an operator to control the movement of mower blade independent of the engine output member. Further, when coupled to an operator presence control, such as a bail, the BBC ensures operator safety by rapidly retarding a mower blade upon release of the bail.
Typically, the components utilized in a clutch are separate and distinct from those employed by a brake and provide a bulky complicated arrangement. For example, in a centrifugal BBC, a clutch drum that can be engaged with a peripheral brake caliper assembly is often used. The clutch drum houses clutch shoes to engage the clutch drum to spin the blade at specified rotational speeds. To brake the clutch drum to prevent rotation after disengagement of the clutch shoes, the brake caliper assembly usually has brake shoes positioned around the side walls of the clutch drum to brake the clutch drum. Thereby, the blade attached to the clutch drum stops rotating.
This type of BBC must be designed to withstand significant mechanical forces applied during operation and may require substantial maintenance. Further, this arrangement creates a large number of parts for assembly as well as for replacement during maintenance. Dimensional constraints are another drawback of conventional BBC control apparatuses. A large surface area is desirable for both the brake and the clutch, however, packaging space often constricts these areas below the optimum values.
Magneto-rheological technology allows for rapid and controllable manipulation of mechanical devices. The apparent viscosity and thus torque capacity of a magneto-rheological fluid is directly proportional to the magnetic flux density applied to it. Therefore, the torque capacity of the fluid can be rapidly controlled by controlling the applied magnetic field.
Therefore, in light of the above, a need exists for clutch control apparatuses and methods that capture the advantages provided by MR technology and are easy to use and operator friendly, so as to allow for the clutching of a power equipment machine while reducing the mechanical complexity, the number of required mechanical parts and the amount of space required for operation.